Re: [PATCH v2 00/15] Make the user mode driver code a better citizen

[Eric W. Biederman]

Alexei Starovoitov <alexei.starovoitov@xxxxxxxxx> writes:

> On Mon, Jun 29, 2020 at 02:55:05PM -0500, Eric W. Biederman wrote:
>> 
>> I have tested thes changes by booting with the code compiled in and
>> by killing "bpfilter_umh" and running iptables -vnL to restart
>> the userspace driver.
>> 
>> I have compiled tested each change with and without CONFIG_BPFILTER
>> enabled.
>
> With
> CONFIG_BPFILTER=y
> CONFIG_BPFILTER_UMH=m
> it doesn't build:
>
> ERROR: modpost: "kill_pid_info" [net/bpfilter/bpfilter.ko] undefined!
>
> I've added:
> +EXPORT_SYMBOL(kill_pid_info);
> to continue testing...
>
> And then did:
> while true; do iptables -L;rmmod bpfilter; done
>  
> Unfortunately sometimes 'rmmod bpfilter' hangs in wait_event().
>
> I suspect patch 13 is somehow responsible:
> +	if (tgid) {
> +		kill_pid_info(SIGKILL, SEND_SIG_PRIV, tgid);
> +		wait_event(tgid->wait_pidfd, !pid_task(tgid, PIDTYPE_TGID));
> +		bpfilter_umh_cleanup(info);
> +	}
>
> I cannot figure out why it hangs. Some sort of race ?
> Since adding short delay between kill and wait makes it work.

Thanks.  I will take a look.

Eric